Device and method for bicompartmental arthroplasty

ABSTRACT

Disclosed is a device and method of bicompartmental arthroplasty of the knee. The device permits arthroplasty of the medial or lateral and patellofemoral compartments of the knee while leaving the opposite compartments and the anterior and posterior cruciate ligaments intact. The device provides a femoral prosthesis component that includes a trochlear surface and a tibial prosthesis component which can be secured to the tibia. The femoral component is essentially “u” shaped having an anterior leg upon which the trochlear surface is positioned and a posterior leg which engages the posterior surface of the distal end of the femur. The femoral component also has a convex articulating surface which engages a concave articulating surface of the tibial prosthesis component to approximate the articulation of a healthy knee. The patellar prosthesis is applied to the posterior surface of the patella and articulates with the trochlear exterior surface of the femur.

PRIORITY INFORMATION

This application is a divisional application of application Ser. No.10/370,002, titled DEVICE AND METHOD FOR BICOMPARTMENTAL ARTHROPLASTY,the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a device and method for bicompartmentalarthroplasty for resurfacing of either the medial joint and thepatellofemoral joint of the knee or the lateral and patellofemoral jointof the knee in order to treat the pain associated with arthritis. Thepresent device and method resurfaces either the medial or lateral jointsdepending on which compartment is diseased, but does not resurface boththe lateral (outside) and medial (inside) compartment of the knee at thesame time.

BACKGROUND OF THE INVENTION

Total knee joint replacement (arthroplasty) is a common and verysuccessful surgery for people with degenerative arthritis(osteoarthritis) of the knee. Over 450,000 patients a year in the UnitedStates undergo total knee replacement surgery. Total knee replacementputs an artificial surface on all parts of the knee joint that contacteach other as the knee bends. The damaged cartilage is removed, a smallamount of bone is removed, the knee implant is attached to the distalend of the femur and proximal end of the tibia, and the patella isresurfaced if necessary. The implant typically is made of metal andplastic and provides an artificial articulating surface which causes nopain to the patient. Unfortunately total knee replacement results insacrifice of the anterior and posterior cruciate ligaments.

More recently, unicompartmental knee arthroplasty has been utilizedwhere there is arthritic damage to only a single compartment of the kneeand no damage to the other compartments. The inside (medial) component(medial tibial plateau and the medial femoral condyle) is most commonlyinvolved and replaced using unicompartmental arthroplasty. However,occasionally, the outside (lateral) compartment (the lateral tibialplateau and the lateral femoral condyle) is sometimes involved and mustbe replaced. Also the knee cap, i.e., the patellofemoral compartment(the patella and femoral trochlear notch) may also developosteoarthritis. Heretofore, if more than a single compartment of theknee had arthritic disease, total knee replacement was the onlyavailable treatment. The present invention provides a device and methodfor bicompartmental arthroplasty which permits the resurfacing of themedial and patellofemoral joints of the knee or the

lateral and patellofemoral joints without the necessity for resurfacingof the opposite compartment of the knee or the sacrifice of the anterioror posterior cruciate ligaments.

BRIEF DESCRIPTION OF THE INVENTION

A device for bicompartmental arthroplasty of a patient's knee inaccordance with the present invention comprises a femoral prosthesiscomponent configured to resurface the patellofemoral and one othercompartment of the knee i.e., either the medial compartment or thelateral compartment depending on which compartment is diseased. Thefemoral prosthesis component has a first internal surface configured tobe secured to a surgically prepared distal end of the one othercompartment of the patient's femur so that the anterior and posteriorcruciate ligaments remain intact. The femoral prosthesis component alsohas a second exterior convex curved surface positioned and configured toreplicate a femoral condyle for that compartment and a concave trochleasurface positioned and configured to articulate with the patella. Thedevice also comprises a tibial prosthesis component configured for theone other compartment of the knee having a first interior surfaceconfigured to be secured to a surgically prepared proximal end of theone other compartment of the patient's tibia and a second concave curvedexterior surface configured to receive the second convex curved surfaceof the femoral prosthesis component to permit pivotal articulationbetween said femoral prosthesis component and the tibial prosthesiscomponent, approximating the articulation of a healthy knee joint.

A method of performing bicompartmental arthroplasty of a patellofemoraland one other compartment of a patient's knee comprises the steps ofmaking an incision along the anterior aspect of the one othercompartment of the knee, excising the remnants of the meniscus of theone other compartment, surgically preparing a proximal end of the oneother compartment of the patient's tibia to receive a tibial prosthesiscomponent in a manner so as to preserve the integrity of the anteriorand posterior cruciate ligaments. The tibial prosthesis component has afirst surface configured to be secured to the surgically prepared oneother compartment of the proximal end of the tibia and a second concavecurved surface. Next the patella is rotated approximately 90 degrees.The distal end of the one other compartment of a the patient's femur issurgically prepared to receive a femoral prosthesis component. Thefemoral prosthesis component has a concave trochlea surface and a firstsurface configured to be secured to the surgically prepared one othercompartment of the distal end of the femur. The femoral component alsohas a second convex curved surface configured to replicate the condyleand articulate with the second concave curved surface of the tibialprosthesis component to permit pivotal articulation between the femoralprosthesis component and the tibial prosthesis component in a mannerapproximating the articulation of a healthy knee joint. The femoralcomponent is next secured to the femur and the tibial component issecured to the tibia. The patella is positioned over the concavetrochlea surface of the femoral prosthesis component and the incision isclosed.

If the patella is also diseased, the method also comprises theadditional steps of surgically preparing a posterior surface of thepatient's patella to receive a patella prosthesis component having afirst surface configured to be secured to the surgically preparedposterior surface of the patella, and a convex curved second surfaceconfigured to engage the concave trochlea surface of the femoralprosthesis component, and securing the patella prosthesis component tothe patella.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of the articular surface of a medialfemoral prosthesis component in accordance with the present invention.

FIG. 1B is a side view of the medial femoral prosthesis component ofFIG. 1.

FIG. 2 is a front view of the medial femoral prosthesis component ofFIG. 1 and a medial tibial prosthesis component of the present inventionas surgically implanted on a human knee.

FIG. 3 is a rear view of a device for bicompartmental arthroplasty ofthe knee in accordance with the present invention as surgicallyimplanted on a human knee.

FIG. 4 is a front view of a device for bicompartmental arthroplasty inaccordance with the present invention as implanted on a human kneeshowing the position of the patella on the device.

FIG. 5 is a front view of a human knee flexed 90° showing the medialfemoral prosthesis component and the medial tibial prosthesis componentimplanted on the knee.

FIG. 6 is a lateral side view of a knee showing the positioning of thepatella and a patella prosthesis component.

FIG. 7 is a side view of a patella component that may be used inconjunction with the present invention.

FIG. 8 is a side view of one type of medial tibial prosthesis componentfor use in connection with the present invention.

FIG. 9 is an upper side perspective view of the prosthesis of FIG. 8.

FIG. 10 is an upper side perspective view of an alternative medialtibial prosthesis component that may be used in connection with thepresent invention.

FIG. 11 is a side view of the prosthesis shown in FIG. 10.

FIG. 12 is a front view of an alternative embodiment of the presentinvention for the lateral compartment of the knee as implanted on ahuman knee.

FIG. 13 is a rear view of the embodiment of FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A and B illustrate a medial femoral prosthesis component 10 foruse in connection with a combination device for bicompartmentalarthroplasty of the knee. The prosthesis 10 is essentially unshaped withone leg of the “u” forming the anterior (front) portion 20 of theprosthesis and the other leg of the “u” forming the posterior (rear)portion 22 of the prosthesis and a base portion 21 connecting theanterior and posterior portions 20 and 22. The medial femoral prosthesiscomponent 10 has an interior first surface 12 which is configured to besecured to a surgically prepared portion of the distal end of the medialcompartment of the femur 26 as shown in FIG. 2 as will be described inmore detail below. The exterior surface 14 of component 10 has a concavetrochlear groove 16 formed on the anterior surface of the leg 20 ofprosthesis component 10. A convex second surface 18 is formed on themedial side of the base portion 21 of prosthesis 10 and is configured toreplicate the medial femoral condyle of the knee. A post 13 is mountedto the interior surface 12 of base portion 21 and extends essentiallyperpendicularly from that surface. Post 13 is inserted into a holedrilled in the femur during surgical preparation to aid in securing thecomponent 10 to the femur 26. More than one post 13 could be mounted todevice 10 as necessary.

With reference to FIG. 2, the prosthesis component 10 is shown inposition as it would be on the distal end of the femur 26 of the humanknee. The anterior leg 20 of the “u” shaped medial component 10 ispositioned over a surgically prepared anterior surface of the femur 26.With reference to FIG. 3, the posterior leg portion 22 of medialcomponent 10 extends upwardly along the posterior surface of asurgically prepared medial compartment of the distal end of the femur26. The interior first surface 12 can be textured to facilitateattachment to the femur using a cement or it may have a bone ingrowthsurface applied so that the bone will grow into the ingrowth surfacethereby securing component 10 to the femur. Prior to implanting, thedistal end of the femur 26 is surgically prepared to remove the diseasedportions of the distal end of the femur and the remnants of the medialmeniscus are excised or removed. The distal end of the femur is then cutto mate with the interior surface 12 of component 10 and a hole isdrilled to accommodate post 13. Alternately, a second hole may bedrilled to accommodate a second post or a keel punch may be used toprepare for a keel in place of the post to secure rotation of thefemoral implant.

With reference to FIG. 2, a medial tibial prosthesis component 28 isshown secured to a surgically prepared portion of the proximal end ofthe tibia. With reference to FIGS. 8 and 9, the medial tibial component28 has a first flat surface 30 and a second concave surface 32. Theconcave surface 32 of the medial tibial component 28 is configured toarticulate with the convex second surface of the medial femoralcomponent 10. Flat surface 30 has a post 31 extending perpendicularlyfrom that surface and is configured and adapted to be secured to asurgically prepared portion of the medial compartment of the tibia 34.Flat surface 30 can be textured to facilitate attachment by cement or itcan have a bone ingrowth surface applied so that the bone will grow intothe ingrowth surface thereby securing the component 28 to the tibia. Asillustrated in FIGS. 2 and 3, a portion of the tibial plateau issurgically removed so that the medial component 28 can be attached. Themedial tibial component 28 illustrated in FIGS. 8 and 9 is comprisedentirely of a plastic material that is biomedically compatible with thehuman body.

FIGS. 10 and 11 illustrate an alternative embodiment of a medial tibialprosthesis component for use in connection with the present invention.The FIG. 10 and 11 component comprises a flat metallic base 36 to whicha plastic insert 38 with a flat base 37 and a concave upper surface 39is attached either rigidly to or to allow rotation or movement upon thefixed base plate 37. The plastic insert 38 can be formed of the sameplastic materials as component 28 illustrated in FIGS. 8 and 9. Metalbase portion 36 has a flat first surface 40 and a downwardly extendingflange 42 along one edge which is designed and configured to extend intoa corresponding groove cut into the posterior surface of the tibia so asto aid in securing base section 36 to the tibia. Surface 40 can eitherbe textured to aid in securing base portion 36 to the tibia using acement, or a bone ingrowth surface can be applied to surface 40 so thatbase portion 36 can be secured to the tibia by bone growth into the boneingrowth surface.

It can be appreciated from FIGS. 2, 3 and 5 that the lateral compartmentof the knee remains in its natural state due to the fact that device 10is affixed only to the medial compartment of the knee. Consequently, theanterior and posterior cruciate ligaments 70 and 72 remain intact andare not compromised by the device 10 or its implantation.

With reference to FIGS. 4 and 6, patella 50 is shown in its normalposition in the trochlear groove 16 of medial femoral component 10. Thepatellar tendon 52 covers the patella and is attached at one end 54 tothe anterior surface of the tibia and the other end 56 to the quadricepsmuscle (not shown). Contraction of the quadriceps muscles pulls thepatella through the trochlear groove, thereby lifting the tibia.

If there is arthritic disease of the patella, it may be necessary toreplace the diseased posterior surface of the patella with a plasticprosthesis component. With reference to FIG. 6, patella 50 is shown indotted lines under the patellar tendon 52. Also shown in dotted lines isa patellar component 58 as it would be positioned in a surgicallyprepared posterior surface of the patella 50. With reference to FIG. 7,a side view of a patella prosthesis component 58 is shown. Patellacomponent 58 is configured to have a convex surface 60 configured anddimensioned to engage and articulate in the trochlea surface 16 of themedial femoral prosthesis component 10. Patellar insert component 58also comprises a surface 62 which includes a post 64 configured andadapted to be secured to a surgically prepared posterior surface of thepatella.

As discussed above, the interior surface 12 of femoral component 10 caneither be configured to be secured to the femur by the use of a cement,or a bone ingrowth surface may be applied to the interior surface 12 sothat the femur bone will grow into and more permanently secure thefemoral component to the femur. Such bone ingrowth surfaces arewell-known in the art and have previously been used in connection withboth unicompartmental and full knee replacement prosthesis. Similarly,the medial tibial prosthesis component 28 can either be secured to thetibia by use of a cement or also by the use of a bone ingrowth surfaceapplied to the tibial component so that the bone structure of the tibiawill grow into the bone ingrowth surface to more permanently secure thetibial component to the tibia.

With reference to FIGS. 3 and 5, it can be seen that the presentinvention can be implanted in the knee without disturbing or damagingthe middle third of the knee joint where the anterior cruciate ligament70 and the posterior cruciate ligament 72 are located. Thus, the presentinvention allows a bicompartmental knee arthroplasty that preserves theintegrity of the anterior and posterior cruciate ligaments.

To implant the FIG. 1-4 embodiment in a patient, a 3 to 4 inchlongitudinal incision is made on the anterior aspect of the knee fromthe medial aspect of the patellar tendon 1 centimeter below the jointline extending approximately 3 to 4 inches in a vertical fashion. Theincision is opened along the length of the incision with a medialparapatellar arthrotomy extending in a minimal fashion into thequadriceps femoris muscle medially. Alternately, a mid vastus or minimid vastus or trivector approach may be employed to arthrotomize theknee joint. The remnants of the medial meniscus are excised. A portionof the fat pad is excised with care being taken to preserve theintegrity of the anterior and posterior cruciate ligaments.

Surface cuts are made on the medial tibial articular surface using thetechnology previously employed by the Accuris® unicompartmentalarthroplasty of Smith and Nephew Orthopedics, Inc. Alternately,intramedullary or extramedullary alignment guides can be employed toguide the medial tibial cuts. After the tibial cut is made, the patellais subluxed or rotated 90°. The intramedullary canal at the distal endof the femur is exposed using a ⅜ inch drill bit. An intramedullary rodis inserted into the distal femur until a distal femoral cutting blockis flush against the distal medial femur. A distal femoral cutting blockof the appropriate angle is attached after the cutting block is pinnedin place, the distal femoral cut is made with an oscillating saw. Thejig is removed and a sizing block is placed against the distal femur inorder to reference the posterior femoral condyles. A stylus is attachedin order to reference the anterior thickness of the distal femur and theappropriate size of the femoral prosthesis 10 is selected, theappropriate femoral cutting block is attached to the intramedullary rodin the appropriate rotation. The block is pinned and the distal anteriorcutting block is used to remove the anterior surface of the distalfemur.

Anterior and posterior chamfer cuts are made from the medial aspect ofthe distal femur followed by a posterior femoral cut for the medialfemoral condyle. The anterior chamfer cut is extended over the medialaspect of the lateral femoral condyle and a sagittal saw is used tocomplete the diagonal cut.

Next, a trial reduction with the femoral component 10 and tibialcomponent 28 is employed to assure correct surgical preparation andsizing. The extent of possible arthritic disease of the patella is nextassessed. If there is extensive disease of the patella, the patella isrotated approximately 90° and an inset patella reamer is applied to theposterior surface of the patella and the patella is reamed to permit theinset of a patella prosthesis component 58. Alternatively, an onset or amobile bearing patella prosthesis may be used as is well known in theart.

A partial lateral facetectomy is typically performed to limit thepatellar contact with the transition zone of the distal femur and thefemoral component 10. The patellar implant 58 should be medialized toassist with patella tracking. Release of the medial collateral ligamentand/or postero-medial structures can be employed as necessary to allowfor ligamentous balancing of the arthroplasty.

The femoral tibial and patellar implants 10 and 28 are next eithercemented in the usual fashion if the trial reduction is found to besatisfactory or securely placed over the prepared bone surface so thatbone ingrowth can occur if the components have a bone ingrowth surfaceapplied. The knee capsule is closed with a non-absorbable suturefollowed by skin closure and sterile metal staples with steriledressing.

With reference to FIGS. 12 and 13, an alternative embodiment of thepresent invention is shown. While in most cases, the medial compartmentof the knee is more prone to be subject to arthritic disease than thelateral compartment, in some cases, the lateral compartment may bediseased while the medial compartment remains healthy and unaffected.This alternative embodiment is designed for those situations where thelateral and patellofemoral joints are affected, but the medialcompartment is not.

A lateral femoral prosthesis component 100 similar to the medial femoralprosthesis component 10 of FIG. 1 except it is configured for thelateral compartment rather than the medial compartment. Lateral femoralprosthesis component 100 is essentially “u” shaped having a firstanterior leg portion 102 and a second posterior leg portion 104 that arejoined by a base portion (not shown). Anterior leg portion 102 has atrochlear groove 106 formed on the face thereof to receive andarticulate with the patella. Lateral femoral prosthesis component 100has an interior surface within the “u” (not shown) similar to theinterior surface 12 of component 10 that can be secured to a surgicallyprepared portion of the lateral compartment of the femur 108 usingeither a cement or a bone ingrowth surface as describe previously.

A lateral tibial prosthesis component 110 similar to the medial tibialcomponent 28 of FIGS. 1-4 is shown in FIGS. 12 and 13 as implanted on asurgically prepared lateral compartment of tibia, 112. Component 110 hasa flat bottom surface and a concave upper surface that receives andarticulates with a convex outer surface (not shown) on the base portionof the femoral prosthesis component 100 in the same manner as describepreviously with respect to the FIG. 1 embodiment. Also, tibial component110 can be fabricated from both metal base and a plastic insert as shownin FIG. 10 and 11.

Femoral component 100 and tibial component 110 are also configured anddesigned so that they can be implanted without causing any damage to themiddle portion of the knee so that the anterior and posterior cruciateligaments remain intact after implantation.

It should be appreciated that both femoral prosthesis components 10 and100 and tibial prosthesis components 28 and 110 can be fabricated fromeither a metallic material or from plastic. Typically, one component isfabricated from one material and the opposing component is fabricatedfrom the other material so that there is a metal on plastic articulatingjoint for wear purposes. However, both parts could be fabricated fromthe same material. A variety of metallic materials can be used includingbut not limited to stainless steel, cobalt chrome steel, titanium,Zirconia, ceramics and tantalum. Also, a variety of plastic materialscan be used including but not limited to polyethylene,polycarbonate-based polyurethane, and implantable-grade polymethylmethacrylate (PMMA).

It should be recognized that the preferred embodiment of the presentinvention as described above can be varied or modified without departingfrom the spirit and scope of the present invention as described andclaimed in the following claims.

1. A method of performing bicompartmental arthroplasty of a patient'sknee comprising the steps of: a. making an incision along the anteriormedial aspect of the knee; b. excising the remnants of the medialmeniscus; c. surgically preparing a medial compartment of a proximal endof the patient's tibia to receive a medial tibial prosthesis componentin a manner so as to preserve the integrity of a anterior and posteriorcruciate ligaments; said medial tibial prosthesis component having afirst surface configured to be secured to said surgically preparedmedial compartment of the proximal end of the patient's tibia and asecond concave curved surface; d. rotating a patella approximately 90degrees; e. surgically preparing a medial compartment of a distal end ofthe patient's femur to receive a medial femoral prosthesis componenthaving a concave trochlea surface; said medial femoral prosthesiscomponent also having a first surface configured to be secured to saidsurgically prepared medial compartment of the distal end of the femurand a second convex curved surface configured to articulate with thesecond concave curved surface of said medial tibial prosthesis componentto permit pivotal articulation between said medial femoral prosthesiscomponent and said medial tibial prosthesis component, said pivotalarticulation approximating the articulation of a healthy knee joint; f.securing a medial femoral component to the femur; g. securing the medialtibial component to the tibia; h. positioning the patella over theconcave trochlea surface of the medial femoral prosthesis component; andi. closing the incision.
 2. A method of performing bicompartmentalarthroplasty of the knee as claimed in claim 1, further comprising theadditional steps of: a. surgically preparing a posterior surface of thepatient's patella to receive a patella prosthesis component having afirst surface configured to be secured to said surgically preparedposterior surface of the patella, and a convex curved second surfaceconfigured to engage the concave trochlea surface of said medial femoralprosthesis component; and b. securing said patella prosthesis componentto the patella.
 3. A method for bicompartmental arthroplasty of the kneeas claimed in claim 1 wherein said medial femoral prosthesis componentcomprises a metallic material.
 4. A method for bicompartmentalarthroplasty of the knee as claimed in claim 1 wherein said medialfemoral prosthesis component comprises a bio-compatible plastic.
 5. Amethod for bicompartmental arthroplasty of the knee as claimed in claim1 wherein said medial tibial prosthesis component comprises abio-compatible plastic.
 6. A method for bicompartmental arthroplasty ofthe knee as claimed in claim 1 wherein said medial tibial prosthesiscomponent comprises a metallic material.
 7. A method for bicompartmentalarthroplasty of the knee as claimed in claim 1 wherein said medialtibial prosthesis component comprises a bio-compatible plastic andmetallic material.
 8. A method for bicompartmental arthroplasty of theknee as claimed in claim 1 wherein said medial femoral prosthesiscomponent and said medial tibial prosthesis component are dimensioned topermit the distal end of the femur and the proximal end of the tibia tobe surgically prepared in manner so as to preserve the integrity of thepatient's anterior and posterior cruciate ligaments.
 9. A method forbicompartmental arthroplasty of the knee as claimed in claim 2 furthercomprising the additional step of: positioning said convex curved secondsurface of said patella prosthesis component to articulate with theconcave trochlea surface of said medial femoral prosthesis component.10. A method for bicompartmental arthroplasty of the knee as claimed inclaim 1 wherein said femoral prosthesis component is secured to thefemur using a cement.
 11. A method for bicompartmental arthroplasty ofthe knee as claimed in claim 1 wherein said femoral prosthesis componentis secured to the femur by bone ingrowth into an ingrowth surfaceapplied to the first surface of the femoral prosthesis component.
 12. Amethod for bicompartmental arthroplasty of the knee as claimed in claim1 wherein said tibial prosthesis component is secured to the tibia usinga cement.
 13. A method for bicompartmental arthroplasty of the knee asclaimed in claim 1 wherein said tibial prosthesis component is securedto the tibia by bone ingrowth into an ingrowth surface applied to thefirst surface of the tibial prosthesis component.
 14. A method forbicompartmental arthroplasty of the knee as claimed in claim 2 whereinsaid patella prosthesis component is secured to the patella by cement.15. A method for bicompartmental arthroplasty of the knee as claimed inclaim 2 wherein said patella prosthesis component is secured to thepatella by bone ingrowth into an ingrowth surface applied to the firstsurface of the patella prosthesis component.
 16. A method of performingbicompartmental arthroplasty of a patient's knee comprising the stepsof: a. making an incision along an anterior medial aspect of the knee;b. excising remnants of a medial meniscus; c. surgically preparing amedial compartment of a proximal end of a patient's tibia to receive amedial tibial prosthesis component in a manner so as to preserve theintegrity of anterior and posterior cruciate ligaments; said medialtibial prosthesis component having a first surface configured to besecured to said surgically prepared medial compartment of the proximalend of the tibia and a second concave curved surface; d. rotating thepatient's patella approximately 90 degrees; e. surgically preparing themedial compartment of a distal end of the patient's femur to receive amedial femoral prosthesis component, said medial femoral prosthesiscomponent having a first leg portion and a second leg portion and a baseportion connected between said first and second leg portions to form anessentially U-shaped component, said medial femoral prosthesis componenthaving a first interior surface configured to be secured to a surgicallyprepared medial compartment of a distal end of the patient's femur sothat a base portion of the femoral prosthesis contacts the distal end ofthe femur, said first leg portion contacts the anterior surface of thedistal end of the femur, and the second leg portion contacts theposterior surface of the distal end of the femur, and said medialfemoral prosthesis component also having a second exterior convex curvedsurface on said base portion, and an exterior concave trochlea surfacepositioned on said first leg portion and configured to articulate withthe patella; said second convex curved surface on said base portionconfigured to articulate with the second concave curved surface of saidmedial tibial prosthesis component to permit articulation between saidmedial femoral prosthesis component and said medial tibial prosthesiscomponent, said articulation motion approximating the articulation of ahealthy knee joint; f. securing the medial femoral component to thefemur; g. securing the medial tibial component to the tibia; h.positioning the patella over the trochlea surface of the medial femoralprosthesis component; and i. closing the incision.
 17. A method ofperforming bicompartmental arthroplasty of the knee as claimed in claim16 comprising the additional steps of: a. surgically preparing aposterior surface of the patient's patella to receive a patellaprosthesis component having a first surface configured to be secured tosaid surgically prepared posterior surface of the patella, and a convexcurved second surface configured to engage the concave trochlea surfaceof said medial femoral prosthesis component; and b. Securing saidpatella prosthesis component to the patella.
 18. A method forbicompartmental arthroplasty of the knee as claimed in claim 16 whereinsaid medial femoral prosthesis component comprises a metallic material.19. A method for bicompartmental arthroplasty of the knee as claimed inclaim 16 wherein said medial femoral prosthesis component comprises abio-compatible plastic.
 20. A method for bicompartmental arthroplasty ofthe knee as claimed in claim 16 wherein said medial tibial prosthesiscomponent comprises a bio-compatible plastic.
 21. A method forbicompartmental arthroplasty of the knee as claimed in claim 16 whereinsaid medial tibial prosthesis component comprises a metallic material.22. A method for bicompartmental arthroplasty of the knee as claimed inclaim 16 wherein said medial tibial prosthesis component comprises abio-compatible plastic and metallic material.
 23. A method forbicompartmental arthroplasty of the knee as claimed in claim 16 whereinsaid medial femoral prosthesis component and said medial tibialprosthesis component are dimensioned to permit the distal end of thefemur and the proximal end of the tibia to be surgically prepared inmanner so as to preserve the integrity of the anterior and posteriorcruciate ligaments.
 24. A method for bicompartmental arthroplasty of theknee as claimed in claim 16 wherein said femoral prosthesis component issecured to the femur using a cement.
 25. A method for bicompartmentalarthroplasty of the knee as claimed in claim 16 wherein said femoralprosthesis component is secured to the femur by bone ingrowth into aningrowth surface applied to the first surface of the femoral prosthesiscomponent.
 26. A method for bicompartmental arthroplasty of the knee asclaimed in claim 16 wherein said tibial prosthesis component is securedto the tibia using a cement.
 27. A method for bicompartmentalarthroplasty of the knee as claimed in claim 16 wherein said tibialprosthesis component is secured to the tibia by bone ingrowth into aningrowth surface applied to the first surface of the tibial prosthesiscomponent.
 28. A method for bicompartmental arthroplasty of the knee asclaimed in claim 17 wherein said patella prosthesis component is securedto the patella by cement.
 29. A method for bicompartmental arthroplastyof the knee as claimed in claim 17 wherein said patella prosthesiscomponent is secured to the patella by bone ingrowth into an ingrowthsurface applied to the first surface of the patella prosthesiscomponent.
 30. A method for bicompartmental arthroplasty of the knee asclaimed in claim 17 further comprising the additional step of:positioning said convex curved second surface of said patella prosthesiscomponent to articulate with the concave trochlea surface of said medialfemoral prosthesis component.